BumGenius one-size worked the best for us. I tried HH, SB, and FB. The problem with all the others is the thighs. Newborn poo leaks out of them so easily when it's not a tight fit. The BG's always gave us a nice close fit.
They are my favorite pocket for all sizes actually. My 4mo and 2yo wear them all the time and I get a great fit on both.